1. Field of the Invention
The present invention relates to excavating beneath a body of water. More particularly, this invention relates to a method an apparatus for providing an improved means for removing a sediment layer from a sand substrate lying below a water surface.
2. Description of the Related Art
The dredging of the bottoms of bodies of water usually takes one of two forms, hydraulic (i.e., suction) dredging or mechanical (bucket loading) dredging. These systems are briefly discussed below.
Hydraulic dredging operations often include a boom or ladder pivotally suspended from a floating vessel to guide the underwater movement of an excavating head or dredging attachment along a bottom surface. The excavated material is removed in a slurry form by suction pressure through a conveying conduit for discharge. Because the percentage solids concentration of such a slurry is relatively low, the operation of such systems has the disadvantage that they often result in large volumes of water that must be treated so as to remove their suspended solids before this water can be returned to its source or discharged off site.
In mechanical dredging systems, buckets extending from a surface vessel are used to “scoop” the bottom material and then raised to the surface where the dredged material is deposited in an adjacent barge or other container capable of receiving the material from the bucket. While the outputs from these systems are at considerable higher percentage solids concentrations, resulting in smaller volumes of water to be treated, they can result in high degrees of contaminants in the surrounding waters as the dredged materials escape from the buckets as they are raised and lowered from the surface.
These systems have often been the subject of patents. For example, see U.S. Pat. Nos. 4,152,800, 4,267,652, 4,307,525, 4,401,576, 4,470,208, 4,631,844, 4,658,751, 4,776,112, 4,957,622, 5,167,841 and 5,732,487.
However, in spite of the extensive prior art in this area, current dredging systems continue to exhibit various limitations in their capabilities. Some of these include the need to: (1) minimize the quantities of intake water that must be treated as a result of a dredging operation, (2) minimize the generation of suspended solids and contaminants in the waters surrounding a dredging site, (3) more precisely remove a varying thickness, sediment layer from an uneven bottom surface, and (4) minimize the effects of varying sea conditions on the preciseness that can be achieved in the dredging operation (i.e., removal of all of the desired mud or other materials without cutting into the underlying bottom surface (e.g., sand substrate)).
Thus, there exists a continuing need for improved dredging methods and apparatus.
3. Objects and Advantages
There has been summarized above, rather broadly, the prior art that is related to the present invention in order that the context of the present invention may be better understood and appreciated. In this regard, it is instructive to also consider the objects and advantages of the present invention.
It is an object of the present invention to provide a method and apparatus for dredging that overcomes the limitations and problems identified with prior dredging systems and methods.
It is another object of the present invention to provide a means for making well determined and controlled thickness dredgings.
It is a yet another object of the present invention to provide a method and apparatus that allow for shallow waters to be effectively dredged.
It is a further object of the present invention to provide a dredging apparatus and method that will have a minimal, negative environmental impact.
These and other objects and advantages of the present invention will become readily apparent as the invention is better understood by reference to the accompanying summary, drawings and the detailed description that follows.